/// 制作z字行下划线
/// @param {String} $index
/// @param {Number} $count
/// @param {Number} $height
/// @param {String} $start_color
/// @param {String} $end_color
/// @author Tony Banik
/// @link https://codepen.io/tonybanik/pen/qMNGJZ

@function mixcolor($index, $count,$height,$start_color,$end_color: $start_color) {
    @if $end_color != $start_color {
        @return mix($end_color, $start_color, percentage($index / (($height * 2) * $count)));
    } @else {
        @return $start_color
    }
}